I don't use it much, because it makes the .dwg heavy/slow, but we have a foto in our titleblock, so I've studied this to to minimize the impact of that.
With INSERTOBJ it's possible to embed an .PDF file, but the resolution is low.
It's better to show the .PDF on screen @ 100% , make a screen capture [WIN+SHIFT+S]. Then INSERTOBJ > PaintBrush > Paste [CTRL+V] > Close Paint